In the measurement art it is known to use a single meter for performing any one of a number of different measurements. Such meters are known as multimeters, and encompass volt-ohm meters (VOM) and vacuum-tube voltmeters (VTVM) as illustrative examples. Multimeters which are digitally controlled, or have digital output displays, are known as digital multimeters (DMM). Prior art DMM's, under control of a programmed controller, are capable of controlling measurement of a particular characteristic of a parameter under test. The resultant measured value is displayed to a predetermined accuracy on a single display.
As is known in the art, readings obtained by measuring devices are subject to a determinable degree of uncertainty, which may be calculated as a function of the magnitude of the parameter being measured and the range, or full scale reading of the meter. A prior art device for calculating an uncertainty associated with a meter reading is known. Such a prior art metering device is capable of displaying only one of the two values of interest to a user. That is, either the measured value of the parameter or the measurement uncertainty is displayed.
However, it is often necessary for a user to know both the measured value and its uncertainty, or other mathematical functions thereof. For example, in a situation where a scaled or offset value of a measured parameter is displayed, the actual parameter value is also of interest. With prior art measuring devices, the user is constrained to determine an offset or scale value, and to rely on his or her own memory to reconvert the displayed scaled or offset value to determine the actual parameter value.
Thus, two sources of error are introduced by the prior art. Firstly, the user's memory may recall an incorrect scaling value for the reconversion. Secondly, the user's capacity for reconversion of the displayed value, by addition or subtraction and/or multiplication or division, may be flawed.
Thus, while prior art DMM's may include sensitive measurement circuitry as well as sophisticated calculation and control circuitry, the equipment is not utilized to its fullest extent. That is, although the programmable controller of a DMM is quite capable of performing various mathematical functions on the measured values, such functions are not performed because of the inability of the meter to display the functional results without at the same time overriding a display of the measured parameter value.
For example, in the above illustration it would be necessary to use two prior art devices for performing the necessary measurement and for providing displays indicative of both the measurement and its uncertainty. A similar requirement is imposed if a user were to desire to utilize the controller to compute another mathematical function of the measured parameter. However, the use of plural devices is expensive.
In order to display simultaneously both the measured value and a mathematical function thereof, two conventional DMM's would be required in order to provide two displays. The DMM's must be arranged to communicate with one another and to permit a controller of one to control the display of the other. Thus, each DMM must be provided with interfacing capability for interfacing and communicating with the other. Moreover, if a conventional DMM were to be used with a separate, auxiliary display, proper interfacing and cabling must be provided, and the display would still require its own controller. Thus, the difficulties and expense associated with providing two displays tend to urge a user to rely on only a single DMM in order to reduce circuit complexity and expenses.
Clearly, measurements performed in such a manner may provide erroneous results, for reasons described above. Additionally, even where a user is possessed of a flawless memory and error free capacity for performing mathematical functions, the values of the measured parameter and its mathematical function are obtained only after substantial time delay. Thus, in those instances where it is necessary for a user to be provided with current easily manipulated information, an expensive arrangement is required in which plural devices are used.
Still another problem with the prior art approach relates to rapidly changing parameters. A user could not himself perform the mathematical functions quickly enough to keep up with the rate at which the meter generates results.
There is thus a need in the prior art for an inexpensive device which is capable of performing a measurement and a mathematical calculation on the measurement result, and which is further capable of providing substantially simultaneous and concurrent displays of the measured value and of a mathematical function.